Fix wrong tag in encoding of SET OF (Closes #30)

src/asn1_types/set/set_of.rs

@@ -140,7 +140,13 @@ where
     }
 
     fn write_der_header(&self, writer: &mut dyn std::io::Write) -> SerializeResult<usize> {
-        self.items.write_der_header(writer)
+        // Do not call self.items.write_der_header(), this will encode the wrong tag (items is a Vec)
+        let mut len = 0;
+        for t in self.items.iter() {
+            len += t.to_der_len().map_err(|_| SerializeError::InvalidLength)?;
+        }
+        let header = Header::new(Class::Universal, true, Self::TAG, Length::Definite(len));
+        header.write_der_header(writer).map_err(Into::into)
     }
 
     fn write_der_content(&self, writer: &mut dyn std::io::Write) -> SerializeResult<usize> {

tests/to_der.rs

@@ -404,6 +404,15 @@ fn to_der_set() {
     assert_eq!(&v, &hex!("31 09 02 01 02 02 01 03 02 01 04"));
 }
 
+#[test]
+fn to_der_set_of() {
+    let seq = SetOf::from_iter([2, 3, 4]);
+    let v = seq.to_der_vec().expect("serialization failed");
+    assert_eq!(&v, &hex!("31 09 02 01 02 02 01 03 02 01 04"));
+    let (_, seq2) = SetOf::from_der(&v).expect("decoding serialized object failed");
+    assert_eq!(seq, seq2);
+}
+
 #[test]
 fn to_der_str() {
     let s = "abcdef";